The discussion below is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
Holding fixtures for three dimensional workpieces are available from Modig Machine AB of Virserum, Sweden and CNA Manufacturing Systems, Inc. of Woodinville, Wash. These fixtures hold workpieces in a fixed position through an array of posts. Each of the posts are equipped with a flexible vacuum cup that when seated upon a portion of the surface of the workpiece forms a vacuum. When a vacuum is pulled in each of the posts, the workpiece is held securely. The posts are arranged in a grid pattern, oriented vertically, such that when the vacuum cups are in a home or resting position each of the vacuum cups lay in a common plane. In order to hold a three dimensional part, each of the posts are adjusted vertically so as to conform the posts taken as a whole to the outer surface of the workpiece to be held. In the Modig System, a large setting machine is provided to adjust the posts. In particular, a gantry setting machine includes two guide rails positioned along opposite sides of the grid of posts and a bridge spanning between the guide rails carries a plurality of setting fixtures used to set the vertical height of each of the posts. As indicated above, the posts are arranged in a grid pattern of equally spaced rows and columns. The setting device, disposed on the bridge, conforms to the row spacing of the posts in the grid. As the bridge moves along the guide rails, the height of each of the setting devices on the bridge is adjusted such that when the corresponding post, located below each setting device, is actuated the post extends upwardly until the desired height of the vacuum cup is obtained. The bridge is moved along the grid on a column-by-column basis setting each column of posts of the grid in this manner. The grid pattern of the posts and the setting bridge may limit the extent of curvature that the workpieces can have.
Another known fixture described in U.S. Pat. No. 7,444,742. The fixture includes a plurality of support assemblies. Each support assembly includes a linear actuator with an end adapted to support a workpiece, or a portion thereof. Each end includes a moveable coupling adapted to hold the workpiece engaging end in a selected orientation. A positioning device is moveable to a position proximate each end of each support assembly, for example, by a robotic arm or other positioning assembly. An end of the positioning device is configured to operate each movable coupling so as to obtain the selected orientation of each end of each support assembly.